Installations using submerged combustion boilers are used for various applications, including industrial heating, swimming pool heating, and the like.
The advantage of such installations is that most of the latent heat of condensation of the vapor is recovered, since the combustion gases are bubbled through the water to be heated. The resulting efficiency, calculated from the lower calorific value, is above 100% and frequently in the order of 105%.
This attractive technique, however, has a number of difficulties inherent in combustion occurring in a submerged medium. The installation requires a fuel supply (e.g. gas or fuel oil), a supply of combustion air pressurized by a fan or the like, an automatic ignition device comprising a spark plug or the like, and a programmer which successively and automatically, at appropriate moments, turns on the fuel supply or the burner ignition or stops the fuel supply when the desired operating temperature has been reached. The burners operate in an enclosed, submerged combustion chamber and consequently, for safety and to avoid any risk of explosion, the air in the chamber has to be scavenged before ignition and after extinction of the boilers. These cycles are controlled by the programmer.
Since, however, the combustion chamber has relatively high thermal inertia and may be brought to temperatures near 1000.degree. C. during combustion, difficulties occur during each operating cycle because water rises into the combustion chamber when it is still hot after post-scavenging, thus subjecting the chamber to severe thermal stresses and possibly cracking it, and vapor and moist air rise through the installation and may interfere with the electric components, including the ignition.